Fabrication in the semiconductor and electronics industries relies on material transfer techniques. Semiconductor device transfer, for example, may be accomplished by a process of mounting and mechanically dicing semiconductor wafers to singulate the devices, followed by a device transfer step using a robotic “pick-and-place” system.
Another process of transferring components supported by a carrier to a desired position on a substrate is described in U.S. Pat. No. 5,941,674, herein incorporated by reference. This process includes moving a carrier including an electronic component to a pick-up position and using an ejector pin such that the component is lifted from the carrier. Simultaneously, a pick-up element is moved towards the component from a site of the carrier remote from the pin, such that the component is picked up by said element by means of vacuum. The component is then moved to a desired position on a substrate by the pick-up element. Such a method is suitable for components whose length and/or width are greater than approximately 0.25 mm and whose thickness is greater than, for example, 70 μm.
Another process suitable for transferring an electronic component supported by a carrier to a desired position on a substrate is described in PCT Patent Application International Publication No. WO 03/101171 A1, herein incorporated by reference. In this process, the carrier supporting the component is moved relative to the substrate while the component is present on a side of the carrier facing the substrate. Then a light beam is directed at the carrier, at the location of the component, from a side remote from the substrate, as a result of which a connection between the component and the carrier is broken and the component is transferred from the carrier to the substrate.
Direct fabrication of miniaturized and rugged electronic devices on a variety of substrates permits rapid prototyping of device concepts and reduced product development design cycle times, and could be used to reduce costs in the manufacturing of such devices. Flexible substrates are particularly attractive for possible roll-to-roll processing of electronic devices (like film based microelectrode sensors arrays), and for processing chemical and biological materials at electronically addressed micro-locations, a variety of displays, and communication devices. Some workers have deposited thin films of amorphous silicon on plastic substrates, for example, but had to subsequently laser-anneal the patterned silicon to render it polycrystalline for high performance devices. Using so-called “fluidic self assembly” (FSA) techniques, multi-device electronic components have been made by repeatedly flowing liquid suspensions of microparticles (individually patterned with single transistors or integrated circuits) over substrates with specially-shaped indentations. The microparticles fit into the indentations to form the completed device. However, this process relies on statistics and requires special equipment.
The term “direct write” refers generally to any technique for creating a pattern directly on a substrate, either by adding or removing material from the substrate, without the use of a mask or preexisting form. Direct write technologies have been developed in response to a need in the electronics industry for a means to rapidly prototype passive circuit elements on various substrates, especially in the mesoscopic regime; that is, electronic devices that straddle the size range between conventional microelectronics (sub-micron-range) and traditional surface mount components (10+ mm-range). Direct writing allows for circuits to be prototyped without iterations in photolithographic mask design and allows the rapid evaluation of the performance of circuits too difficult to accurately model. Since most direct write processes operate in ambient environment, high-rate production processes (such as roll-to-roll and sheet-to-sheet processes) can be enabled for electronic components that previously had to be processed in batches under controlled environments such as vacuum. Further, direct writing allows for the size of printed circuit boards and other structures to be reduced by allowing passive circuit elements to be conformably incorporated into the structure. Direct writing can be controlled with CAD/CAM programs, thereby allowing electronic circuits to be fabricated by machinery operated by unskilled personnel or allowing designers to move quickly from a design to a working prototype. Other applications of direct write technologies in microelectronics fabrication include forming ohmic contacts, forming interconnects for circuit and device restructuring, and customization.
In the direct writing technique known as “laser induced forward transfer” (LIFT), a pulsed laser beam is directed through a laser-transparent target substrate to strike a film of material coated on the opposite side of the target substrate. The laser-irradiated film of material vaporizes or ablates as it absorbs the laser radiation and, due to the transfer of momentum, the material is removed from the target substrate and is redeposited on a receiving substrate that is placed in proximity to the target substrate. Laser induced forward transfer is typically used to transfer opaque thin films (e.g., metals) from a pre-coated laser transparent support (typically glass, SiO2, Al2O3, SrTiO3, etc.) to the receiving substrate.
Because the film material is vaporized by the action of the laser, laser induced forward transfer is inherently a homogeneous, pyrolytic technique and typically cannot be used to deposit complex crystalline, multi-component materials or materials that have a crystallization temperature well above room temperature because the resulting deposited material will be a weakly-adherent amorphous coating. Moreover, because the material to be transferred is vaporized, it becomes more reactive and can more easily become degraded, oxidized or contaminated. The method is not well suited for the transfer of organic materials, since many organic materials are fragile and thermally labile and can be irreversibly damaged during deposition. For example, functional groups on an organic polymer can be irreversibly damaged by direct exposure to laser energy. Other disadvantages of the laser induced forward transfer technique include poor surface-coverage uniformity, morphology, adhesion and resolution. Further, because of the high temperatures involved in the process, there is a danger of ablation or sputtering of the support which can cause the incorporation of impurities in the material that is deposited on the receiving substrate. Another disadvantage of laser induced forward transfer is that it typically requires that the coating of the material to be transferred be a thin coating, generally less than 1 micron thick. Because of this requirement, it is very time -consuming to transfer more than very small amounts of material.
To avoid direct vaporization of the material to be transferred, the following variation of the laser induced forward transfer technique may be employed. The laser -transparent substrate is coated with several layers of materials, or with a coating that is a mixture of the material of interest in a matrix of other materials. In this layered approach, the outermost layer (that is, the layer closest to the receiving substrate) consists of the material to be deposited and the innermost layer consists of a material that absorbs laser energy and becomes vaporized, causing the outermost layer to be propelled against the receiving substrate. Matrix assisted pulsed laser evaporation direct write (MAPLE-DW) is one technique which utilizes this approach and has been used to transfer materials such as metals, ceramics, and polymers onto polymeric, metallic, and ceramic substrates at room temperature. A disadvantage of this method is that, because many materials were present on the laser-transparent substrate, it is difficult to achieve a highly homogeneous coating of the material of interest. A homogeneous coating would be required, for example, for the construction of electronic devices, sensing devices or passivation coatings.
Currently, the most advanced generation of semiconductor devices employs geometries of 0.13 microns with ˜100 nm gate lengths and ˜1.5 nm gate oxide thicknesses. Integrated circuit (IC) devices with these feature sizes (and associated high-performance) cannot be fabricated using direct write technologies. However, this is not problematic in that the IC device fabrication infrastructure is already well-established.
Devices are normally transferred via “pick and place” robotic systems. Pick and place systems typically transfer die that are pre-packaged in a rectangular plastic “lead frame” with metallic legs, i.e., such as the die visible on the motherboard in your computer. Pick and place systems may also handle so-called “bare” or “unpackaged” die. There is a need to develop methods that may be used to transfer a large number of devices on a flexible or curved substrate without having to reposition the wafer. A pick and place system can only transfer one device at a time, and cannot handle putting devices across a large area with high accuracy.
Therefore, there is a need for materials and methods for rapidly transferring pre -fabricated electronic devices and unpatterned electronic materials (including single layers and multiple layers of these devices and materials) to flexible and curved substrates with retention of device/material properties. There is a need for a process that makes use of off-the-shelf wafers based on crystalline Si, wafers with buried layers (such as silicon-on-insulator (SOI) wafers), and high-performance such as, GaAs, SiGe and InP wafers.
There remains a need to provide rapid transfer of pre-formed devices in electronic fabrication. There remains a need to develop materials and methods in which a consumable intermediate may be used in fabrication, especially in late-stage processing. Because the costs of fabricating/building on a flexible or curved substrate are very high, there remains a need to transfer a pre-formed device onto a flexible or curved substrate as a late-stage processing step.